Memory access alignment in a double data rate (‘DDR’) system

ABSTRACT

Memory access alignment in a double data rate (‘DDR’) system, including: executing, by a memory controller, one or more write operations to a predetermined address of a DDR memory module, including sending to the DDR memory module a predetermined amount of data of a predetermined pattern along with a data strobe signal; executing, by the memory controller, a plurality of read operations from the predetermined address of the DDR memory module, including capturing data transmitted from the DDR memory module; and determining, by the memory controller, a read adjust value and a write adjust value in dependence upon the data captured in response to the read operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application and claimspriority from U.S. patent application Ser. No. 14/011,030, filed Aug.27, 2013, which is a divisional application and claims priority fromU.S. patent application Ser. No. 13/171,811, filed Jun. 29, 2011, nowU.S. Pat. No. 8,547,760, issued Oct. 1, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, apparatus, and products for memory access alignment in a doubledata rate (DDR) system.

2. Description Of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

In a DDR system, DRAMs send a strobe (DQS) coincident with multiplebeats of data (DV). On reads, the memory controller chip is responsiblefor delaying the DQS to capture the DQ bits while meeting the setup andhold requirements at the capturing latches. On writes, the memorycontroller chip is responsible for delaying the DQS to be ideallycentered within the DQ “eye” to ensure proper capture into the memorydevice. Before a DRAM device is used to store actual application data,the memory controller runs a training sequence where DQS and DQ arrivaltimes at both the DRAM and memory controller are measured againstreference clocks. These measurements are then used to adjust DQS and DQdelays to meet setup and hold times. As DRAM speeds increase, thelikelihood of crossing a clock edge gets higher so the need to ensurealignment to the correct clock edge becomes greater.

SUMMARY OF THE INVENTION

Methods, apparatus, and products for memory access alignment in a doubledata rate (‘DDR’) system, including: executing, by a memory controller,one or more write operations to a predetermined address of a DDR memorymodule, including: signaling the DDR memory module of the one or morewrite operations; and sending to the DDR memory module a predeterminedamount of data of a predetermined pattern along with a data strobesignal; executing, by the memory controller, a plurality of readoperations from the predetermined address of the DDR memory module,including: signaling the DDR memory module of the read operations;capturing data transmitted from the DDR memory module; and determining,by the memory controller, a read adjust value and a write adjust valuein dependence upon the data captured in response to the read operations,wherein the read adjust value is a number of cycles between signalingthe read operations and capturing a specific portion of thepredetermined data pattern, and wherein the write adjust value is anumber of cycles between signaling the DDR memory module of the one ormore write operations and sending to the DDR memory module thepredetermined amount of data of the predetermined pattern along with thedata strobe signal.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of example embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of example embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth a block diagram of automated computing machinerycomprising an example computer useful in memory access alignment in aDDR system according to embodiments of the present invention.

FIG. 2 sets forth a flow chart illustrating an example method for memoryaccess alignment in a DDR system according to embodiments of the presentinvention.

FIG. 3 sets forth a flow chart illustrating an example method for memoryaccess alignment in a DDR system according to embodiments of the presentinvention.

FIG. 4 sets forth a flow chart illustrating an example method foridentifying, by the memory controller, a read adjust value and a writeadjust value in dependence upon the data received from the one or moreread commands according to embodiments of the present invention.

FIG. 5 sets forth a flow chart illustrating an example method for memoryaccess alignment in a DDR system according to embodiments of the presentinvention.

FIG. 6 sets forth a timing diagram of example read operations in a DDRsystem configured for memory access alignment in a DDR system.

FIG. 7 sets forth a timing diagram of example write operations in a DDRsystem configured for memory access alignment in a DDR system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Example methods, apparatus, and products for memory access alignment ina double data rate (‘DDR’) system in accordance with the presentinvention are described with reference to the accompanying drawings.Memory access alignment in a DDR system in accordance with the presentinvention is generally implemented with computers, that is, withautomated computing machinery. For further explanation, therefore, FIG.1 sets forth a block diagram of automated computing machinery comprisingan example computer (152) useful in memory access alignment in a DDRsystem according to embodiments of the present invention. The computer(152) of FIG. 1 includes at least one computer processor (156) or ‘CPU’as well as DDR synchronous dynamic random access memory (168) (‘DDRSDRAM’) which is connected through a high speed memory bus (166) and busadapter (158) to processor (156) and to other components of the computer(152).

Stored in the DDR SDRAM (168) is an operating system (154). Operatingsystems useful for memory access alignment in a DDR system according toembodiments of the present invention include UNIX™, Linux™, MicrosoftXP™, AIX™, IBM's i5/OS™, and others as will occur to those of skill inthe art. The operating system (154) in the example of FIG. 1 is shown inDDR SDRAM (168), but many components of such software typically arestored in non-volatile memory also, such as, for example, on a diskdrive (170).

The computer (152) of FIG. 1 includes disk drive adapter (172) coupledthrough expansion bus (160) and bus adapter (158) to processor (156) andother components of the computer (152). Disk drive adapter (172)connects non-volatile data storage to the computer (152) in the form ofdisk drive (170). Disk drive adapters useful in computers for memoryaccess alignment in a DDR system according to embodiments of the presentinvention include Integrated Drive Electronics (‘IDE’) adapters, SmallComputer System Interface (‘SCSI’) adapters, and others as will occur tothose of skill in the art. Non-volatile computer memory also may beimplemented for as an optical disk drive, electrically erasableprogrammable read-only memory (so-called ‘EEPROM’ or ‘Flash’ memory),RAM drives, and so on, as will occur to those of skill in the art.

The example computer (152) of FIG. 1 includes one or more input/output(‘I/O’) adapters (178). I/O adapters implement user-orientedinput/output through, for example, software drivers and computerhardware for controlling output to display devices such as computerdisplay screens, as well as user input from user input devices (181)such as keyboards and mice. The example computer (152) of FIG. 1includes a video adapter (209), which is an example of an I/O adapterspecially designed for graphic output to a display device (180) such asa display screen or computer monitor. Video adapter (209) is connectedto processor (156) through a high speed video bus (164), bus adapter(158), and the front side bus (162), which is also a high speed bus.

The example computer (152) of FIG. 1 includes a communications adapter(167) for data communications with other computers (110) and for datacommunications with a data communications network (100). Such datacommunications may be carried out serially through RS-232 connections,through external buses such as a Universal Serial Bus (‘USB’), throughdata communications networks such as IP data communications networks,and in other ways as will occur to those of skill in the art.Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a data communications network.Examples of communications adapters useful in systems that carry outmemory access alignment in a DDR system according to embodiments of thepresent invention include modems for wired dial-up communications,Ethernet (IEEE 802.3) adapters for wired data communications networkcommunications, and 802.11 adapters for wireless data communicationsnetwork communications.

The example computer (152) of FIG. 1 also includes a memory controller(200). The memory controller (200) of FIG. 1 is a circuit that managesthe flow of data going to and from memory. In the example of FIG. 1, thememory controller (200) manages the flow of data to and from one or moreDDR memory modules, embodied here as the DDR SDRAM (168). In the exampleof FIG. 1, the memory controller (200) is depicted as residing withinthe bus adapter (158). Readers will appreciate that the memorycontroller (200) may be a standalone unit, included in DDR modulesthemselves, included in a northbridge or southbridge, on amicroprocessor, or embodied in other ways as will occur to those ofskill in the art.

The computer (152) of FIG. 1 is an example of a DDR system as the termis used in this specification. In the example of DDR system (152) ofFIG. 1, memory access alignment in a DDR system in accordance withembodiments of the present invention includes executing, by the memorycontroller (200), one or more write operations to a predeterminedaddress of a DDR memory module. In the example of FIG. 1, executing oneor more write operations to a predetermined address of a DDR memorymodule includes signaling the DDR memory module of the one or more writeoperations and sending to the DDR memory module a predetermined amountof data of a predetermined pattern along with a data strobe signal.

In the example of FIG. 1, memory access alignment in a DDR system (152)in accordance with embodiments of the present invention also includesexecuting, by the memory controller, a plurality of read operations fromthe predetermined address of the DDR memory module. In the example ofFIG. 1, executing a plurality of read operations from the predeterminedaddress of the DDR memory module includes signaling the DDR memorymodule of the read operations and capturing data transmitted from theDDR memory module.

In the example of FIG. 1, memory access alignment in a DDR system (152)in accordance with embodiments of the present invention also includesdetermining, by the memory controller, a read adjust value and a writeadjust value in dependence upon the data captured in response to theread operations. In the example of FIG. 1, the read adjust value is anumber of cycles to adjust a read latency interval between signaling theread operations and capturing the data. In the example of FIG. 1, thewrite adjust value is a number of cycles to adjust a write latencyinterval between signaling the DDR memory module of the one or morewrite operations and sending to the DDR memory module the predeterminedamount of data of the predetermined pattern along with the data strobesignal.

For further explanation, FIG. 2 sets forth a flow chart illustrating anexample method for memory access alignment in a DDR system according toembodiments of the present invention that includes executing (202), by amemory controller (200), one or more write operations to a predeterminedaddress of a DDR memory module (201). In the example of FIG. 2, thememory controller (200) is a circuit that manages the flow of data goingto and from memory, such as one or more DDR memory modules (201).Although the example described in FIG. 2, as well as the remainingfigures of the present application, is described in the context of theDDR protocol, the concepts described herein can be applied to any DDRbased protocol such as DDR2, DDR3, DDR4, QDR, RLDRAM, LLDRAM, and so on.

In the example of FIG. 2, executing (202), by a memory controller (200),one or more write operations to a predetermined address of a DDR memorymodule (201) includes signaling the DDR memory module of the one or morewrite operations and sending to the DDR memory module a predeterminedamount of data of a predetermined pattern along with a data strobesignal. In the example of FIG. 2, executing (202) a single writeoperation would consist of a write command being issued to the DDRmemory module (i.e., “signaling the DDR memory module of the writeoperation”) and later in time, driving data to the DDR memory module(i.e., “sending to the DDR memory module a predetermined amount ofdata”). That is, a single write operation may be viewed as consisting oftwo coupled parts—a write command and the data that is to be written.

In the example of FIG. 2, executing (202) one or more write operationsto a predetermined address of a DDR memory module (201) includessignaling (204) the DDR memory module (201) of the one or more writeoperations. Signaling (204) the DDR memory module (201) may be carriedout, for example, by asserting a signal across a command control linebetween the memory controller (200) and the DDR memory module (201). Insuch an example, the DDR memory module (201) may be configured suchthat, after determining that the command control line has been asserted,the DDR memory module (201) stores data asserted on data signal lines ata memory location specified by an address asserted on address signallines. That is, the command control line, for a write command, initiatesthe storage of data at a memory location.

In the example of FIG. 2, executing (202) one or more write operationsto a predetermined address of a DDR memory module (201) also includessending (206) to the DDR memory module (201) a predetermined amount ofdata (208) of a predetermined pattern along with a data strobe signal.In the example of FIG. 2, a data strobe signal is bi-directional signalthat is used to initiate read operations from a DDR memory module (201)and write operations to the DDR memory module (201). For write commands,the pulses of the data strobe signal are used as clock signals by a DDRmemory module (201) to capture the corresponding input data for a writecommand which, in the example of FIG. 2, is embodied as thepredetermined amount of data (208).

In the example of FIG. 2, the predetermined amount of data (208)associated with the one or more write commands represents that data thatis to be written to the predetermined address as the result of the oneor more write commands. In the example of FIG. 2, sending (206) to theDDR memory module (201) a predetermined amount of data (208) of apredetermined pattern along with a data strobe signal may be carriedout, for example, by sending the predetermined amount of data (208) anda predetermined number of pulses of the data strobe signal over a memorybus.

The predetermined amount of data (208) of FIG. 2 may include datagenerated according to a predetermined pattern. For example, thepredetermined amount of data (208) of FIG. 2 may include data generatedaccording to a predetermined pattern that is characterized by increasingnumerical values. For example, consider an embodiment in which thepredetermined amount of data (208) is sixteen bytes. In such an example,the first two bytes of the predetermined amount of data (208) may be anumerical ‘0,’ the second two bytes of the predetermined amount of data(208) may be a numerical ‘1,’ and so on such that the predeterminedamount of data (208) is characterized by a numerical pattern of‘00112233.’ In such an example, because the values in the pattern don'tuse all available bits within a nibble or a byte, the algorithm canstill be used in situations where bits are bad and have been masked off.For example, if another algorithm has discovered and marked a bit asbad, the algorithm can still work if the bad bit is masked off and datais steered away from the bad bit since all the values from hex 0 to hex7 only require 3 bits and a fourth bad bit within a nibble can simply bemasked off and steered around.

The example of FIG. 2 also includes executing (210), by the memorycontroller (200), a plurality of read operations from the predeterminedaddress of the DDR memory module (201). In the example of FIG. 2,executing (210) a plurality of read operations from the predeterminedaddress of the DDR memory module (201) includes signaling (212) the DDRmemory module (201) of the read operations. Signaling (212) the DDRmemory module (201) may be carried out, for example, by deasserting asignal across a command control line between the memory controller (200)and the DDR memory module (201). In such an example, the DDR memorymodule (201) may be configured such that, after determining that thecommand control line has been deasserted, the DDR memory module (201)reads data from a memory location specified by an address asserted onaddress signal lines. That is, the command control line when deassertedinitiates the reading of data from a memory location. In such anexample, the DDR memory module (201) subsequently places (205) the readdata (214) on a data line for transmission to the memory controller(200).

In the example of FIG. 2, executing (210) a plurality of read operationsfrom the predetermined address of the DDR memory module (201) alsoincludes capturing (216) data transmitted from the DDR memory module(201). In the example of FIG. 2, the memory controller (200) operates tocapture (216) at least some portion of the read data (214) sent from theDDR memory module (201). Such data may be captured, for example, byreading a data line between the DDR memory module (201) and the memorycontroller (200).

The example of FIG. 2 also includes determining (218), by the memorycontroller (200), a read adjust value and a write adjust value independence upon the data captured in response to the read operations. Inthe example of FIG. 2, the read adjust value is a number of cycles toadjust a read latency interval between signaling (212) the readoperations and capturing (216) the data. In the example of FIG. 2, theremay be a delay between the time when the DDR memory module signals (212)the read operations and the time that the read data (214) is availablefor reading at the memory controller (200). This delay is referred to inthis specification as the read latency interval. The read latencyinterval may exist because the DDR memory module (201) needs some amountof time to identify that a read operation is requested, the DDR memorymodule (201) needs some amount of time to retrieve the requested data,the DDR memory module (201) needs some amount of time to place (205) theread data (214) on a data line, and other similar reasons. In theexample of FIG. 2, the read adjust value represents the number of cyclesthat the read latency interval should be adjusted so as to ensure propertiming.

In the example of FIG. 2, the write adjust value is a number of cyclesto adjust a write latency interval between signaling (204) the DDRmemory module (201) of the one or more write operations and sending(206) to the DDR memory module (201) the predetermined amount of data(208) of the predetermined pattern along with the data strobe signal. Inthe example of FIG. 2, there may be need to be a delay between the timewhen the DDR memory module signals (204) the DDR memory module (201) ofthe one or more write operations and sends (206) to the DDR memorymodule (201) the predetermined amount of data (208) of the predeterminedpattern along with the data strobe signal. This delay is referred to inthis specification as the write latency interval. The write latencyinterval may exist because the DDR memory module (201) needs some amountof time to receive and process a request to perform a write operation.In the example of FIG. 2, the write adjust value represents the numberof cycles that the write latency interval should be adjusted so as toensure proper timing. Determining (218), by the memory controller (200),a read adjust value and a write adjust value in dependence upon the datacaptured in response to the read operations will be described in greaterdetail in the remaining figures.

For further explanation, FIG. 3 sets forth a flow chart illustrating anexample method for memory access alignment in a DDR system according toembodiments of the present invention. The example of FIG. 3 is similarto the example of FIG. 2 as the example of FIG. 3 also includesexecuting (202), by a memory controller (200), one or more writeoperations to a predetermined address of a DDR memory module (201),including signaling (204) the DDR memory module (201) of the one or morewrite operations and sending (206) to the DDR memory module (201) apredetermined amount of data (208) of a predetermined pattern along witha data strobe signal. The example of FIG. 3, like the example of FIG. 2,also includes executing (210), by the memory controller (200), aplurality of read operations from the predetermined address of the DDRmemory module (201), including signaling (212) the DDR memory module(201) of the read operations and capturing (216) data transmitted fromthe DDR memory module (201). The example of FIG. 3, like the example ofFIG. 2, also includes determining (218), by the memory controller (200),a read adjust value and a write adjust value in dependence upon the datacaptured in response to the read operations. In the example of FIG. 3,the read adjust value is a number of cycles to adjust a read latencyinterval between signaling (212) the read operations and capturing (216)the data. In the example of FIG. 3, the write adjust value is a numberof cycles to adjust a write latency interval between signaling (204) theDDR memory module (201) of the one or more write operations and sending(206) to the DDR memory module (201) the predetermined amount of data ofthe predetermined pattern along with the data strobe signal.

In the example of FIG. 3, however, executing (202) one or more writeoperations to a predetermined address of the DDR memory module (201)also includes determining (302), by the memory controller (200), theburst length for the write operations. In the example of FIG. 3, theburst length for a write command represents the number of bytes that areto be written to an address in response to a single write command.Different versions of DDR memory modules may be associated withdifferent burst lengths such that determining (302), by the memorycontroller (200), the burst length for a write command may be carriedout, for example, by identifying whether the target DDR memory module isa DDR1 memory module, DDR2 memory module, DDR 3 memory module, and soon.

In the example of FIG. 3, executing (202) one or more write operationsto a predetermined address of the DDR memory module (201) also includesdetermining (304), by the memory controller (200), a number of writeoperations to execute in dependence upon the burst length. For example,DDR3 has a burst length of eight (‘BL8’) such that each read operationreads eight bytes of data and each write operation writes eight bytes ofdata. Memory access alignment in a DDR system may be carried out,however, for different versions of DDR memory modules by taking intoaccount the burst length associated with the different versions of DDR.For example, rather than issuing a single BL8 command to a DDR memorymodule, the memory controller (200) may alternatively issue two burstlength four (‘BL4’) write commands to the DDR memory module.Furthermore, different burst lengths may be utilized not for the purposeof mimicking a single BL8 but rather for adapting the present inventionfor different systems and embodiments. In embodiments in which the burstlength is not BL8, different patterns of numerical values may be used toidentify the read latency and write latency for a particular system.

The example of FIG. 3 also includes storing (308), by the memorycontroller (200), the read adjust value. In the example of FIG. 3, theread adjust value may be stored (308), for example, in computer memoryon the memory controller (200) itself or in computer memory otherwiseaccessible to the memory controller (200).

The example of FIG. 3 also includes increasing (312), by the read adjustvalue, the number of cycles between signaling subsequent read operationsand capturing data from the subsequent read operations. As discussedabove, the read adjust value is a number of cycles to adjust a readlatency interval between signaling (212) the read operations andcapturing (216) the data. In the example of FIG. 3, adjusting the readlatency interval may be carried out by increasing the number of cyclesbetween signaling subsequent read operations and capturing data from thesubsequent read operations by a number of cycles that is equal to theread adjust value for subsequently issued read commands.

The example of FIG. 3 also includes storing (306), by the memorycontroller (200), the write adjust value. In the example of FIG. 3, thewrite adjust value may be stored (306), for example, in computer memoryon the memory controller (200) itself or in computer memory otherwiseaccessible to the memory controller (200).

The example of FIG. 3 also includes increasing (310), by the writeadjust value, the number of cycles between signaling the DDR memorymodule of subsequent write operations and sending to the DDR memorymodule data associated with the subsequent write operations along withthe data strobe signal. As discussed above, the write adjust value is anumber of cycles to adjust a write latency interval between signaling(204) the DDR memory module (201) of the one or more write operationsand sending (206) to the DDR memory module (201) the predeterminedamount of data (208) of the predetermined pattern along with the datastrobe signal. In the example of FIG. 3, adjusting the write latencyinterval may be carried out by increasing the number of cycles betweensignaling the DDR memory module (201) of the subsequent write operationsand sending to the DDR memory module data associated with the subsequentwrite operations along with the data strobe signal. Although the exampleof FIG. 3 describes increasing (310) the number of cycles betweensignaling the DDR memory module of subsequent write operations andsending to the DDR memory module data associated with the subsequentwrite operations, readers will appreciate that using different patternsof numerical values would allow the number of cycles between signalingthe DDR memory module and sending to the DDR memory module dataassociated with the subsequent write operations to be decreased in otherembodiments of the present invention. In such embodiments a ‘negativeadjust’ may be utilized for memory access alignment in a DDR systemaccording to embodiments of the present invention.

For further explanation, FIG. 4 sets forth a flow chart illustrating anexample method for memory access alignment in a DDR system according toembodiments of the present invention. The example of FIG. 4 is similarto the example of FIG. 2 as the example of FIG. 4 also includesexecuting (202), by a memory controller (200), one or more writeoperations to a predetermined address of a DDR memory module (201),including signaling (204) the DDR memory module (201) of the one or morewrite operations and sending (206) to the DDR memory module (201) apredetermined amount of data (208) of a predetermined pattern along witha data strobe signal. The example of FIG. 4, like the example of FIG. 2,also includes executing (210), by the memory controller (200), aplurality of read operations from the predetermined address of the DDRmemory module (201), including signaling (212) the DDR memory module(201) of the read operations and capturing (216) data transmitted fromthe DDR memory module (201). The example of FIG. 4, like the example ofFIG. 2, also includes determining (218), by the memory controller (200),a read adjust value and a write adjust value in dependence upon the datacaptured in response to the read operations. In the example of FIG. 4,the read adjust value is a number of cycles to adjust a read latencyinterval between signaling (212) the read operations and capturing (216)the data. In the example of FIG. 4, the write adjust value is a numberof cycles to adjust a write latency interval between signaling (204) theDDR memory module (201) of the one or more write operations and sending(206) to the DDR memory module (201) the predetermined amount of data ofthe predetermined pattern along with the data strobe signal.

In the example of FIG. 4, however, executing (202), by a memorycontroller (200), one or more write operations to a predeterminedaddress of a DDR memory module (201) includes signaling (402) only asingle write operation. In the example of FIG. 4, the single writeoperation that is signaled (402) is a BL8 write operation. As describedabove with reference to FIG. 2, a single write operation may be viewedas consisting of two coupled parts—a write command and the data that isto be written. In the example of FIG. 4, signaling (402) only a singlewrite operation may include issuing, by the memory controller, two writeoperations but only signaling the DDR memory module (201) of one of thewrite operations. As such, although only a single write operation issignaled (402), more than a single operation's worth of data may stillbe sent to the DDR memory module (201) such that the DDR memory module(201) receives only one write command but still receives enough data fortwo write commands.

In the example of FIG. 4, sending (206) to the DDR memory module (201) apredetermined amount of data of a predetermined pattern along with adata strobe signal includes sending (404) two burst lengths of data. Inthe example of FIG. 4, given that a single BL8 write command is beingsignaled (402) as described above, the burst length is therefore eightbytes. In such an example, sending (404) two burst lengths of datatherefore includes sending sixteen bytes of data in spite of the factthat only eight bytes of data are needed for execution of the single BL8write operation. As described above with reference to FIG. 2, a singlewrite operation may be viewed as consisting of two coupled parts—a writecommand and the data that is to be written. The benefit of sending (404)two burst lengths of data will become apparent below.

In the example of FIG. 4, the write data (208) sent (206) to the DDRmemory module (201) is of a predetermined pattern. In the example ofFIG. 4, the predetermined pattern includes numerical values from 0 to 7organized incrementally. As discussed above, two burst lengths of dataare being sent (404) according to the predetermined pattern describedabove. The write data (208) of a predetermined pattern may therefore beembodied as sixteen bytes of data, where the first byte and second byteof data are a numerical ‘0’, the third byte and the fourth byte of dataare a numerical ‘1’, the fifth byte and sixth byte of data is anumerical ‘2’, and so on such that the sixteen bytes of data are asfollows: 0011223344556677. Although this sixteen byte pattern is sent(206) to the DDR memory module (201), only eight bytes of this data willbe written to the DDR memory module (201) as only a single BL8 writeoperation is being signaled (402). By determining which eight bytes werewritten to the DDR memory module (201), a write adjust value can bedetermined (218) as described in more detail below.

In the example of FIG. 4, capturing (216) data transmitted from the DDRmemory module (201) includes capturing (406) only one burst length ofdata. As discussed above, a plurality of read operations are beingexecuted (210). In the example of FIG. 4, each read operation is a BL8read operation. Although at least two read operations are being executedby the DDR memory module (201), only one burst length of data is beingcaptured (406) by the memory controller (200). The memory controller(200) may capture (406) only one burst length of data by only initiatingone read_ start operation at the memory controller (200), where theread_ start operation causes the memory controller to begin listening tothe pertinent control, signal, and data lines. By determining whicheight bytes were captured (406) by the memory controller (200), a readadjust value can be determined (218) as described in more detail below.

For further explanation, FIG. 5 sets forth a flow chart illustrating anexample method for determining (218), by the memory controller (201), aread adjust value and a write adjust value in dependence upon the datacaptured in response to the read operations according to embodiments ofthe present invention. As described above, a data strobe signal isbi-directional signal that is used to initiate read operations from aDDR memory module (201) and write operations to the DDR memory module(201). For write operations, the data strobe signal is generated by thememory controller (200) that initiated the write operation. A DDR memorymodule (201) that receives a write signal from the memory controller(200) will read data on a data line upon receipt of the data strobesignal from the memory controller (200). In particular, the DDR memorymodule (201) that receives a write signal from a memory controller (200)will read data on the data line at both the rising edge of a data strobesignal pulse and also at the falling edge of a data strobe signal pulse.

For read operations, the data strobe signal is generated by the DDRmemory module (201) that is transferring the read data (214) in responseto a read signal received from the memory controller (200). A memorycontroller (200) that initiates a read operation will read data from adata line upon receipt of a data strobe signal from the DDR memorymodule (201). The data that the memory controller (200) reads from adata line is data placed on the data line by the DDR memory module (201)in response to the read operation. In particular, the memory controller(200) that initiates a read operation will read data from a data line atboth the rising edge of a data strobe signal pulse and also at thefalling edge of a data strobe signal pulse.

In view of the fact that the data strobe signal can be sent from thememory controller (200) to the DDR memory module (201) or sent from theDDR memory module (201) to the memory controller (200), the data strobesignal is said to be bi-directional. Because the data strobe signal isused to initiate read operations from the DDR memory module (201) andwrite operations to the DDR memory module (201), however, a writelatency may exist such that the memory controller (200) delays sendingthe data strobe signal to the DDR memory module (201) when initiatingwrite operations so that the DDR memory module (201) reads the correctdata off of the data line upon receipt of the data strobe signal pulses.Likewise, a read latency may exist such that the memory controller (200)delays reading from a data line after initiating a read operation so asto give the DDR memory module (201) an appropriate amount of time toplace read data (214) on a data line. The write latency and read latencymay need to be increased to ensure proper timing. In the example of FIG.5, the number of cycles that the write latency and read latency need tobe increased is identified as the write adjust value and read adjustvalue respectively.

The example of FIG. 5 describes determining (218), by the memorycontroller (201), a read adjust value and a write adjust value independence upon the data captured in response to the read operations isdescribed in a particular context. The example of FIG. 5 describesdetermining (218) a read adjust value and a write adjust value in anexample in which the steps described in FIG. 4 were carried out. Thatis, the example of FIG. 5 assumes the following:

-   -   The memory controller (200) executed a single BL8 write command        in which data was written to the DDR memory module (201) as        described above with reference to FIG. 4;    -   the memory controller (200) sent sixteen bytes worth of data to        the DDR memory module (201) over a data line while also sending        pulses of the data strobe signal to the DDR memory module (201)        as described above with reference to FIG. 4;    -   the sixteen bytes of data sent by the memory controller (200) to        the DDR memory module (201) included numerical values of 0, 0,        1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, and 7 as described above        with reference to FIG. 4, and    -   the memory controller (200) executed two BL8 read commands to        read data from the predetermined address and the memory        controller (200) also captured only eight bytes of the read data        (214) as described above with reference to FIG. 4.

In the example of FIG. 5, the memory controller (200) may determine(218) a read adjust value and a write adjust value in dependence uponthe read data (214) received from the one or more read operations. Inthe example of FIG. 5, the memory controller (200) may determine (218) aread adjust value and a write adjust value by segmenting (502) the eightbytes of read data (214) that were captured by the memory controller(200) into memory controller (200) four two-value pairs.

In the example of FIG. 5, the memory controller (200) may determine(218) a read adjust value and a write adjust value in dependence uponthe data (214) received from the one or more read commands bydetermining (504), whether a numerical value in a first unit of thecaptured data is greater than a numerical value in a second unit of thecaptured data. In the example of FIG. 5, the first unit of the captureddata is the first two-value pair and the second unit of the captureddata is the second two-value pair. If the numerical value in the firsttwo-value pair read by the memory controller (200) is (505) greater thanthe numerical value in the second two-value pair read by the memorycontroller (200), the memory controller can set (506) the read adjustvalue to one cycle and also set (506) the write adjust value to thevalue of the numerical value contained in the second two-value pair.

In the example of FIG. 5, the numerical value in the first two-valuepair read by the memory controller (200) may only be greater than thenumerical value in the second two-value pair read by the memorycontroller (200) when the memory controller (200) is reading: 1) thelast two-value pair placed on the data line from the first BL8 readcommand, and 2) the first three two-value pairs placed on the data linefrom the second BL8 read command.

In the example in which the numerical value in the first two-value pairread by the memory controller (200) is greater than the numerical valuein the second two-value pair read by the memory controller (200), theread adjust value should be set (506) to one cycle such that the readlatency interval between signaling the read operations and capturing theread data is increased by one cycle. Furthermore, when the numericalvalue in the first two-value pair read by the memory controller (200) isgreater than the numerical value in the second two-value pair read bythe memory controller (200), the write adjust value should be set to thevalue of the numerical value contained in the second two-value pair readby the memory controller (200). Consider two situations: 1) a firstsituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were perfectly timed, and 2) asecond situation in which signaling the DDR memory module (201) of theone or more write operations and sending write data and the data strobesignal pulses to the DDR memory module (201) were not perfectly timed.

In the situation in which signaling the DDR memory module (201) of theone or more write operations and sending write data and the data strobesignal pulses to the DDR memory module (201) were perfectly timed,because a single BL8 write operation was executed and followed by a datastream of numerical values of 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,7, and 7, the DDR memory module (201) would have stored values of 0, 0,1, 1, 2, 2, 3, and 3 at the predetermined address. In such an example,the first BL8 read operation would place 0, 0, 1, 1, 2, 2, 3, and 3 onthe data line and the second BL8 read operation would also place 0, 0,1, 1, 2, 2, 3, and 3 on the data line. In order for the numerical valuein the first two-value pair read by the memory controller (200) to begreater than the numerical value in the second two-value pair read bythe memory controller (200), the memory controller (200) would need toread two-value pair values of 33, 00, 11, 22. In other words, thenumerical value in the first two-value pair read by the memorycontroller (200) may only be greater than the numerical value in thesecond two-value pair read by the memory controller (200) when thememory controller (200) is reading: 1) the last two-value pair placed onthe data line from the first BL8 read operation, and 2) the first threetwo-value pairs placed on the data line from the second BL8 readoperation.

The read adjust value should therefore be set (506) to one cycle suchthat the read latency interval between signaling the read operations andcapturing the read data is increased by one cycle. Furthermore, thewrite adjust value should be set to the value of the numerical valuecontained in the second two-value pair read by the memory controller(200). In this case that value is ‘0’, which is to be expected in thesituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were perfectly timed.

Alternatively, in the second situation in which signaling the DDR memorymodule (201) of the one or more write operations and sending write dataand the data strobe signal pulses to the DDR memory module (201) werenot perfectly timed, the approach still works. Consider, for example,that sending write data and the data strobe signal pulses to the DDRmemory module (201) needed to be delayed by two cycles such that the DDRmemory module (201) would have stored the values of 2, 2, 3, 3, 4, 4, 5,and 5 (i.e., the values of 0, 0, 1, and 1 that were placed on the dataline were gone when the DDR memory module (201) began reading from thedata line in response to the data strobe signal pulses) at thepredetermined address. The first BL8 read operation would thereforeplace 2, 2, 3, 3, 4, 4, 5, and 5 on the data line and the second BL8read operation would also place 2, 2, 3, 3, 4, 4, 5, and 5 on the dataline. In order for the numerical value in the first two-value pair readby the memory controller (200) to be greater than the numerical value inthe second two-value pair read by the memory controller (200), thememory controller (200) would need to read two-value pair values of 55,22, 33, and 44. In other words, the numerical value in the firsttwo-value pair read by the memory controller (200) may only be greaterthan the numerical value in the second two-value pair read by the memorycontroller (200) when the memory controller (200) is reading: 1) thelast two-value pair placed on the data line from the first BL8 eadoperation, and 2) the first three two-value pairs placed on the dataline from the second BL8 read operation.

The read adjust value should therefore be set to one cycle such that theread latency interval between signaling the read operations andcapturing the read data is increased by one cycle. Furthermore, thewrite adjust value should be set to the value of the numerical valuecontained in the second two-value pair read by the memory controller(200). In this case that value is ‘2’, which is to be expected in thesituation in which the data and data strobe signal needed to be delayedby two additional cycles.

In the example of FIG. 5, the memory controller (200) may also determine(218) a read adjust value and a write adjust value by determining (508),whether a numerical value in a second unit of the captured data isgreater than a numerical value in a third unit of the captured data. Inthe example of FIG. 5, the second unit of the captured data is thesecond two-value pair and the third unit of the captured data is thethird two-value pair. If the numerical value in the second two-valuepair read by the memory controller (200) is (509) greater than thenumerical value in the third two-value pair read by the memorycontroller (200), the memory controller can set (510) the read adjustvalue to two cycles and also set (510) the write adjust value to thenumerical value contained in the third two-value pair.

In the example of FIG. 5, the numerical value in the second two-valuepair read by the memory controller (200) may only be greater than thenumerical value in the third two-value pair read by the memorycontroller (200), after making the determination described in step 504,when the memory controller (200) is reading: 1) the last two two-valuepairs placed on the data line from the first BL8 read operation, and 2)the first two two-value pairs placed on the data line from the secondBL8 read operation.

In the example in which the numerical value in the second unit of thecaptured data is greater than the numerical value in the third unit ofthe captured data, the read adjust value should be set (506) to twocycles such that the read latency interval between signaling the readoperations and capturing the read data is increased by two cycles.Furthermore, when the numerical value in the second two-value pair readby the memory controller (200) is greater than the numerical value inthe third two-value pair read by the memory controller (200), aftermaking the determination made in step 504, the write adjust value shouldbe set to the numerical value contained in the third two-value pair readby the memory controller (200). Consider two situations: 1) a firstsituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were perfectly timed, and 2) asecond situation in which signaling the DDR memory module (201) of theone or more write operations and sending write data and the data strobesignal pulses to the DDR memory module (201) were not perfectly timed.

In the first situation in which signaling the DDR memory module (201) ofthe one or more write operations and sending write data and the datastrobe signal pulses to the DDR memory module (201) were perfectlytimed, because a single BL8 write operation was executed and followed bya data stream of numerical values of 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,6, 6, 7, and 7, the DDR memory module (201) would have stored values of0, 0, 1, 1, 2, 2, 3, and 3 at the predetermined address. In such anexample, the first BL8 read operation would place 0, 0, 1, 1, 2, 2, 3,and 3 on the data line and the second BL8 read operation would alsoplace 0, 0, 1, 1, 2, 2, 3, and 3 on the data line. In order for thenumerical value in the second two-value pair read by the memorycontroller (200) to be greater than the numerical value in the thirdtwo-value pair read by the memory controller (200), after making thedetermination described in step 504, the memory controller (200) wouldneed to read two-value pair values of 22, 33, 00, and 11. In otherwords, the numerical value in the second two-value pair read by thememory controller (200) may only be greater than the numerical value inthe third two-value pair read by the memory controller (200), aftermaking the determination described in step 504, when the memorycontroller (200) is reading: 1) the last two two-value pairs placed onthe data line from the first BL8 read operation, and 2) the first twotwo-value pairs placed on the data line from the second BL8 readoperation.

The read adjust value should therefore be set (510) to two cycles suchthat the read latency interval between signaling the read operations andcapturing the read data is increased by two cycles. Furthermore, thewrite adjust value should be set to the value of the numerical valuecontained in the third two-value pair read by the memory controller(200). In this case that value is ‘0’, which is to be expected in thesituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were perfectly timed.

Alternatively, in the second situation in which signaling the DDR memorymodule (201) of the one or more write operations and sending write dataand the data strobe signal pulses to the DDR memory module (201) werenot perfectly timed, the approach still works. Consider, for example,that sending write data and the data strobe signal pulses to the DDRmemory module (201) needed to be delayed by three cycles such that theDDR memory module (201) would have stored values of 3, 3, 4, 4, 5, 5, 6,and 6 (i.e., the values of 0, 0, 1, 1, 2, and 2 that were placed on thedata line were gone when the DDR memory module (201) began reading fromthe data line in response to the data strobe signal pulses) at thepredetermined address. The first BL8 read operation would thereforeplace 3, 3, 4, 4, 5, 5, 6, and 6 on the data line and the second BL8read operation would also place 3, 3, 4, 4, 5, 5, 6, and 6 on the dataline. In order for the numerical value in the second two-value pair readby the memory controller (200) to be greater than the numerical value inthe third two-value pair read by the memory controller (200), the memorycontroller (200) would need to read two-value pair values of 55, 66, 33,and 44. In other words, the numerical value in the second two-value pairread by the memory controller (200) may only be greater than thenumerical value in the third two-value pair read by the memorycontroller (200), after making the determination described in step 504,when the memory controller (200) is reading: 1) the last two two-valuepair placed on the data line from the first BL8 read operation, and 2)the first two two-value pairs placed on the data line from the secondBL8 read operation.

The read adjust value should therefore be set (510) to two cycles suchthat the read latency interval between signaling the read operations andcapturing the read data is increased by two cycles. Furthermore, thewrite adjust value should be set (510) to the value of the numericalvalue contained in the third two-value pair read by the memorycontroller (200). In this case that value is ‘3’, which is to beexpected in the situation in which the data strobe signal needed to bedelayed by three additional cycles.

In the example of FIG. 5, the memory controller (200) may also determine(218) a read adjust value and a write adjust value by determining (512),whether a numerical value in a third unit of the captured data isgreater than a numerical value in a fourth unit of the captured data. Inthe example of FIG. 5, the third unit of the captured data is the thirdtwo-value pair and the fourth unit of the captured data is the fourthtwo-value pair. If the numerical value in the third two-value pair readby the memory controller (200) is (515) greater than the numerical valuein the fourth two-value pair read by the memory controller (200), thememory controller can set (514) the read adjust value to three cyclesand also set (514) the write adjust value to the numerical valuecontained in the fourth two-value pair.

In the example of FIG. 5, the numerical value in the third two-valuepair read by the memory controller (200) may only be greater than thenumerical value in the fourth two-value pair read by the memorycontroller (200), after making the determinations described in steps 504and 508, when the memory controller (200) is reading: 1) the last threetwo-value pairs placed on the data line from the first BL8 readoperation, and 2) the first two-value pair placed on the data line fromthe second BL8 read operation.

In an example in which the numerical value in the third two-value pairread by the memory controller (200) is greater than the numerical valuein the fourth two-value pair read by the memory controller (200), theread adjust value should be set (514) to three cycles such that the readlatency interval between signaling the read operations and capturing theread data is increased by three cycles. Furthermore, when the numericalvalue in the third two-value pair read by the memory controller (200) isgreater than the numerical value in the fourth two-value pair read bythe memory controller (200), after making the determinations made insteps 504 and 508, the write adjust value should be set to the numericalvalue contained in the fourth two-value pair read by the memorycontroller (200). Consider two situations: 1) a first situation in whichsignaling the DDR memory module (201) of the one or more writeoperations and sending write data and the data strobe signal pulses tothe DDR memory module (201) were perfectly timed, and 2) a secondsituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were not perfectly timed.

In the first situation in which signaling the DDR memory module (201) ofthe one or more write operations and sending write data and the datastrobe signal pulses to the DDR memory module (201) were perfectlytimed, because a single BL8 write operation was executed and followed bya data stream of numerical values of 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5,6, 6, 7, and 7, the DDR memory module (201) would have stored values of0, 0, 1, 1, 2, 2, 3, and 3 at the predetermined address. The first BL8read operation would therefore place 0, 0, 1, 1, 2, 2, 3, and 3 on thedata line and the second BL8 read operation would also place 0, 0, 1, 1,2, 2, 3, and 3 on the data line. In order for the numerical value in thethird two-value pair read by the memory controller (200) to be greaterthan the numerical value in the fourth two-value pair read by the memorycontroller (200), after making the determinations described in steps 504and 508, the memory controller (200) would need to read two-value pairvalues of 11, 22, 33, and 00. In other words, the numerical value in thethird two-value pair read by the memory controller (200) may only begreater than the numerical value in the fourth two-value pair read bythe memory controller (200), after making the determinations describedin steps 504 and 508, when the memory controller (200) is reading: 1)the last three two-value pairs placed on the data line from the firstBL8 read operation, and 2) the first two-value pair placed on the dataline from the second BL8 read operation.

The read adjust value should therefore be set (510) to three cycles suchthat the read latency interval between signaling the read operations andcapturing the read data is increased by three cycles. Furthermore, thewrite adjust value should be set to the value of the numerical valuecontained in the fourth two-value pair read by the memory controller(200). In this case that value is ‘0’, which is to be expected in thesituation in which signaling the DDR memory module (201) of the one ormore write operations and sending write data and the data strobe signalpulses to the DDR memory module (201) were perfectly timed.

Alternatively, in the second situation in which signaling the DDR memorymodule (201) of the one or more write operations and sending write dataand the data strobe signal pulses to the DDR memory module (201) werenot perfectly timed, the approach still works. Consider, for example,that sending write data and the data strobe signal pulses to the DDRmemory module (201) needed to be delayed by one cycle such that the DDRmemory module (201) would have stored values of 1, 1, 2, 2, 3, 3, 4, and4 (i.e., the values of 0 and 0 that were placed on the data line weregone when the DDR memory module (201) began reading from the data linein response to the data strobe signal pulses) at the predeterminedaddress. The first BL8 read operation would therefore place 1, 1, 2, 2,3, 3, 4, and 4 on the data line and the second BL8 read operation wouldalso place 1, 1, 2, 2, 3, 3, 4, and 4 on the data line. In order for thenumerical value in the third two-value pair read by the memorycontroller (200) to be greater than the numerical value in the fourthtwo-value pair read by the memory controller (200), the memorycontroller (200) would need to read two-value pair values of 22, 33, 44,and 11. In other words, the numerical value in the third two-value pairread by the memory controller (200) may only be greater than thenumerical value in the fourth two-value pair read by the memorycontroller (200), after making the determinations described in steps 504and 508, when the memory controller (200) is reading: 1) the last threetwo-value pairs placed on the data line from the first BL8 readoperation, and 2) the first two-value pair placed on the data line fromthe second BL8 read operation.

The read adjust value should therefore be set (514) to three cycles suchthat the read latency interval between signaling the read operations andcapturing the read data is increased by three cycles. Furthermore, thewrite adjust value should be set (514) to the value of the numericalvalue contained in the fourth two-value pair read by the memorycontroller (200). In this case that value is ‘1’, which is to beexpected in the situation in which the data strobe signal needed to bedelayed by one additional cycle.

In the event that the memory controller (200) determines (504) that thenumerical value in the first two-value pair is not (407) greater thanthe numerical value in the second two-value pair, and subsequentlydetermines (508) that the numerical value in the second two-value pairis not (411) greater than the numerical value in the third two-valuepair, and subsequently determines (512) that the numerical value in thethird two-value pair is not (415) greater than the numerical value inthe fourth two-value pair, the read adjust value is set (516) to zerocycle and the write adjust value is set (516) to the value of thenumerical value contained in the first two-value pair.

In the example of FIG. 5, if the numerical value of the first two-valuepair is not (507) greater than the numerical value of the secondtwo-value pair, the numerical value of the second two-value pair is not(511) greater than the numerical value of the third two-value pair, andthe numerical value of the third two-value pair is not (515) greaterthan the numerical value of the fourth two-value pair, then the memorycontroller (200) is reading: 1) the entire contents of the second BL8read operation, or 2) the entire contents of the first BL8 readoperation at an ‘aliased position’. Although the present applicationonly presents examples and delay capabilities based on the memorycontroller reading the entire contents of the second BL8 read operationin this situation, the reader will appreciate that larger delaysrequired to handle the aliased position could be accounted for andaddressed by adapting the algorithm to a larger pattern or by making useof another coarse adjustment method when the aliased condition isdetected.

In an example in which the memory controller (200) is reading the entirecontents of the second BL8 read operation, the read adjust value shouldbe set (516) to zero cycles. Furthermore, the write adjust value shouldbe set to the value of the numerical value contained in the firsttwo-value pair read by the memory controller (200). Consider twosituations: 1) a first situation in which signaling the DDR memorymodule (201) of the one or more write operations and sending write dataand the data strobe signal pulses to the DDR memory module (201) wereperfectly timed, and 2) a second situation in which signaling the DDRmemory module (201) of the one or more write operations and sendingwrite data and the data strobe signal pulses to the DDR memory module(201) were not perfectly timed

In the first situation in which signaling the DDR memory module (201) ofthe one or more write operations and sending write data and the datastrobe signal pulses to the DDR memory module (201) were perfectlytimed, because a single BL8 write operation was issued to apredetermined address and followed by a data stream of numerical valuesof 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, and 7, the DDR memorymodule (201) would have stored values of 0, 0, 1, 1, 2, 2, 3, and 3 atthe predetermined address. The first BL8 read operation would thereforeplace 0, 0, 1, 1, 2, 2, 3, and 3 on the data line and the second BL8read operation would also place 0, 0, 1, 1, 2, 2, 3, and 3 on the dataline. In order to make all of the “No” (507, 511, 515) determinationsdescribed in steps 504, 508, and 512, the memory controller (200) wouldneed to read two-value pair values of 00, 11, 22, and 33. In otherwords, the memory controller (200) is reading the four two-value pairsplaced on the data line from the second BL8 read operation.

The read adjust value should therefore be set (516) to zero cycles suchthat the read latency interval between signaling the read operations andcapturing the read data is not altered. Furthermore, the write adjustvalue should be set (516) to the value of the numerical value containedin the first two-value pair read by the memory controller (200). In thiscase that value is ‘0’, which is to be expected in the situation inwhich signaling the DDR memory module (201) of the one or more writeoperations and sending write data and the data strobe signal pulses tothe DDR memory module (201) were perfectly timed.

Alternatively, in the second situation in which signaling the DDR memorymodule (201) of the one or more write operations and sending write dataand the data strobe signal pulses to the DDR memory module (201) werenot perfectly timed, the approach still works. Consider, for example,that sending write data and the data strobe signal pulses to the DDRmemory module (201) needed to be delayed by four cycles such that theDDR memory module (201) would have values of 4, 4, 5, 5, 6, 6, 7, and 7(i.e., the values of 0, 0, 1, 1, 2, 2, 3, and 3 that were placed on thedata line were gone when the DDR memory module (201) began reading fromthe data line in response to the data strobe signal pulses) at thepredetermined address. The first BL8 read operation would thereforeplace 4, 4, 5, 5, 6, 6, 7, and 7 on the data line and the second BL8read operation would also place 4, 4, 5, 5, 6, 6, 7, and 7 on the dataline. In order to make all of the “No” (507, 511, 515) determinationsdescribed in steps 504, 508, and 512 the memory controller (200) wouldneed to read two-value pair values of 44, 55, 66, and 77. In otherwords, the memory controller (200) is reading the four two-value pairsplaced on the data line from the second BL8 read operation.

The read adjust value should be set (516) to zero cycles such that theread latency interval between signaling the read operations andcapturing the read data is not altered. Furthermore, the write adjustvalue should be set to the value of the numerical value contained in thefirst two-value pair read by the memory controller (200). In this casethat value is ‘4’, which is to be expected in the situation in which thedata strobe signal needed to be delayed by four additional cycles.

For further explanation, FIG. 6 sets forth a timing diagram of exampleread operations in a DDR system configured for memory access alignmentin a DDR system. The timing diagram includes two examples: example 1(600) and example 2 (601). Example 1 (600) illustrates an example inwhich the read latency interval between signaling the read operationsand capturing the data is ideal. In other words, example 1 (600)illustrates an example in which the read adjust value would be set tozero. Example 2 (601) illustrates an example in which the read latencyinterval between signaling the read operations and capturing the data isone cycle too short. In other words, example 2 (601) illustrates anexample in which the read adjust value would be set to one.

Example 1 (600) illustrates a memory clock line (602), a command line(604), a read start line (606), a data strobe signal line (608), a dataline (610), and a read window line (612). Example 2 (601) alsoillustrates a memory clock line (614), a command line (616), a readstart line (618), a data strobe signal line (620), a data line (622),and a read window line (624).

In the example of FIG. 6, the memory clock lines (602, 614) representclock signals generated by a memory clock. The command lines (604, 616)of FIG. 6 represent the status of a bus that runs between a memorycontroller and DDR memory module for signaling the DDR memory module ofa read operation to be performed. In the example of FIG. 6, the commandlines (604, 616) depict the signaling of read operations that are beinginitiated, by a memory controller, between the memory controller and aDDR memory module. A memory controller may signal a DDR memory module ofsuch read operations, for example, by transferring an address to the DDRmemory module from which data is to be read from. In example 1 (600) andexample 2 (601), two read operations are signaled to the DDR memorymodule, operations labeled as ‘Read 1’ and ‘Read 2’.

In the example of FIG. 6, the read start lines (606, 618) arerepresentations of a timing mechanism used by a memory controller toinitiate reading from a data bus between the memory controller and a DDRmemory module. In the example of FIG. 6, a pulse on the read start lines(606, 618) represents a read start command. In the example of FIG. 6,the read start command causes a memory controller to begin reading froma data bus between the memory controller and a DDR memory module a setnumber of cycles after the read start command has been issued. In theparticular example of FIG. 6, however, the read start command takes timeto execute, such that a memory controller doesn't begin capturing dataoff of the data line until a set number of cycles after initiating theread start command. This delay is referred to herein the ‘capturedelay’. In the example of FIG. 6, the capture delay is one cycle asillustrated by the relative timing of the read start command and theread window that is described in more detail below.

In the example of FIG. 6, the data strobe signal lines (608, 620) arerepresentations of data strobe signal pulses that are sent from a DDRmemory module to a memory controller as a part of a read operationinitiated by the memory controller. In such an example, the memorycontroller will read data on the data line at both the falling edge andrising edge of a data strobe signal pulse.

In the example of FIG. 6, the data lines (610, 622) are representationsof the state of a memory bus that runs between a memory controller and aDDR memory module. The data lines (610, 622) depict particular bytes ofdata that are being transferred from a DDR memory module to the memorycontroller in response to a read operation initiated by the memorycontroller. In example 1 (600) and example 2 (601), byte values of 0, 0,1, 1, 2, 2, 3, and 3 are placed on the memory bus by the DDR memorymodule in response to the first read operation labeled as ‘Read 1’. Inexample 1 (600) and example 2 (601), the second read operation labeledas ‘Read 2’ also causes the DDR memory module to place byte values of 0,0, 1, 1, 2, 2, 3, and 3 on the data (610) line, although only a subsetof these bytes are illustrated in FIG. 6.

In the example of FIG. 6, the read window lines (612, 624) represent thewindow in which a memory controller reads from a data bus runningbetween the memory controller and the DDR memory module. The example ofFIG. 6 depicts an embodiment in which BL8 read operations are executed,such that the memory controller reads eight bytes of data off of thedata bus to complete a read operation. Therefore, the read windows areeight bytes in burst length.

In the example of FIG. 6, the read latency for the DDR system that thetiming diagram of FIG. 6 corresponds to is two cycles. The read latencyfor the DDR system represents the number of cycles between the time atwhich a DDR memory module was signaled of a read operation and the timeat which the DDR memory module placed data on a data bus in response tothe read operation.

In the example of FIG. 6, example 1 (600) depicts a perfectly timed readoperation. In example 1 (600), a read operation, ‘Read 1’, is signaledand two cycles later the DDR memory module has begun data strobe signalpulsing and has placed data on a data bus, as a result of a read latencyin the DDR system of two cycles as described above. In example 1 (600),a read start command was issued one cycle after the time that the readoperation ‘Read 2’ was signaled. Because there is a capture delay of onecycle, as described above, the memory controller begins capturing dataoff of the data bus one cycle later as illustrated by the read window.In example 1 (600), the DDR memory module has placed data on the databus at the same time that the memory controller begins to capture datafrom the memory bus, thereby causing the memory controller to perfectlycapture the data transmitted from the DDR memory module in response toread operation ‘Read 2’. In such an example, the read adjust value iszero and there is no adjustment needed between the time at which thememory controller signals the DDR memory module of a read operation andthe time at which the memory controller captures the data placed on thedata bus as a result of the read operation.

In the example of FIG. 6, however, example 2 (601) depicts animperfectly timed read operation. In example 2 (601), a read operation,‘Read 2’, is signaled and two cycles later the DDR memory module hasbegun data strobe signal pulsing and has placed data on a data bus, as aresult of a read latency in the DDR system of two cycles as describedabove. In example 2 (601), a read start command was issued one cycleafter the read operation ‘Read 2’ was signaled to the DDR memory module.Because there is a capture delay of one cycle, as described above, thememory controller begins capturing data off of the data bus one cyclelater as illustrated by the read window. In example 2 (601), the DDRmemory module has placed data on the data bus after the memorycontroller begins to capture data from the memory bus, thereby causingthe memory controller to capture the last two bytes of data transmittedfrom the DDR memory module in response to read operation ‘Read 1’ andalso to capture the first six bytes of data transmitted from the DDRmemory module in response to read operation ‘Read 2’. In such anexample, the read adjust value is one, signifying that an adjustment ofone cycle is needed between the time at which the memory controllersignals the DDR memory module of a read operation and the time at whichthe memory controller captures the data placed on the data bus as aresult of the read operation. The memory controller may make thisadjustment by issuing the read start command one cycle later relative tosignaling the DDR memory module of the read operation.

For further explanation, FIG. 7 sets forth a timing diagram of examplewrite operations in a DDR system configured for memory access alignmentin a DDR system. The timing diagram includes two examples: example 1(700) and example 2 (701). Example 1 (700) illustrates an example inwhich the write latency interval between signaling the DDR memory moduleof one or more write operations and sending to the DDR memory module thedata associated with such write operations is ideal. In other words,example 1 (700) illustrates an example in which the write adjust valuewould be set to zero. Example 2 (701) illustrates an example in whichthe write latency interval between signaling the DDR memory module ofone or more write operations and sending to the DDR memory module thedata associated with such write operations is one cycle too short. Inother words, example 2 (701) illustrates an example in which the writeadjust value would be set to one.

Example 1 (700) illustrates a memory clock line (702), a command line(704), a data strobe signal line (706), a data line (708), and a writewindow line (710). Example 2 (701) also illustrates a memory clock line(712), a command line (714), a data strobe signal line (716), a dataline (718), and a write window line (720).

In the example of FIG. 7, the memory clock lines (702, 712) representclock signals generated by a memory clock. The command lines (704, 714)of FIG. 7 represent the status of a bus that runs between a memorycontroller and DDR memory module for signaling the DDR memory module ofa write operation to be performed. In the example of FIG. 7, the commandlines (704, 714) depict the signaling of a write operation that is beinginitiated, by a memory controller, between the memory controller and aDDR memory module. A memory controller may signal a DDR memory module ofsuch write operations, for example, by transferring an address to theDDR memory module that data is to be written to. In example 1 (700) andexample 2 (601), one write operation is signaled to the DDR memorymodule, operations labeled as ‘Write 1’.

In the example of FIG. 7, the data strobe signal lines (706, 716) arerepresentations of data strobe signal pulses that are sent from a memorycontroller to a DDR memory module as a part of a write operationinitiated by the memory controller. In such an example, the DDR memorymodule will read data (i.e., the data to be written to the DDR memorymodule) on the data line at both the falling edge and rising edge of adata strobe signal pulse.

In the example of FIG. 7, the data lines (708, 718) are representationsof the state of a memory bus that runs between a memory controller and aDDR memory module. The data lines (708, 718) depict particular bytes ofdata that are being transferred from a memory controller to DDR memorymodule as part of a write operation initiated by the memory controller.In example 1 (700) and example 2 (701), byte values of 0, 0, 1, 1, 2, 2,3, 3, 4, 4, 5, 5, 6, 6, 7, and 7 are placed on the memory bus by thememory controller as part of the write operation labeled as ‘Write 1’,although only a subset of these bytes are illustrated in FIG. 7.

In the example of FIG. 7, the write window lines (710, 720) representthe window in which a DDR memory module reads data (i.e., the data beingwritten to the DDR memory module) from a data bus running between thememory controller and the DDR memory module. The example of FIG. 7depicts an embodiment in which BL8 read operations are executed, suchthat the DDR memory module reads eight bytes of data off of the data busto complete a write operation. Therefore, the write windows are eightbytes in burst length.

In the example of FIG. 7, the write latency for the DDR system that thetiming diagram of FIG. 7 corresponds to is three cycles. The writelatency for the DDR system represents the number of cycles between thetime at which a DDR memory module was signaled of a write operation andthe time at which the DDR memory module begins reading data on a databus in response to the write operation. In such an example, the DDRmemory module begins reading data on a data bus for the purposes ofwriting such data to the DDR memory module.

In the example of FIG. 7, example 1 (700) depicts a perfectly timedwrite operation. In example 1 (700), a write operation, ‘Write 1’, issignaled to the DDR memory module and three cycles later the DDR memorymodule begins reading data on a data bus in response to the writeoperation, as a result of a write latency in the DDR system of threecycles as described above. In example 1 (700), the memory controller hasbegun data strobe signal pulsing and has also placed data on the dataline three cycles after signaling the write command to the DDR memorymodule, thereby causing the DDR memory module to perfectly capture thedata transmitted to the DDR memory module as part of write operation‘Write 1’. In such an example, the write adjust value is zero and thereis no adjustment needed between the time at which the memory controllersignals the DDR memory module of a write operation and the time at whichthe memory controller begins data strobe signal pulsing and placing dataon the data bus.

In the example of FIG. 7, however, example 2 (701) depicts animperfectly timed write operation. In example 2 (701), a writeoperation, ‘Write 1’, is signaled to the DDR memory module and threecycles later the DDR memory module begins reading data on a data bus inresponse to the write operation, as a result of a write latency in theDDR system of three cycles as described above. In example 2 (701), thememory controller has begun data strobe signal pulsing and has alsoplaced data on the data line two cycles after signaling the writecommand to the DDR memory module, thereby causing the DDR memory moduleto miss capturing first two bytes of data associated with the writeoperation ‘Write 1’. In such an example, the write adjust value is oneand the time between signaling the DDR memory module of the one or morewrite operations and sending to the DDR memory module data associatedwith the write operation along with the data strobe signal should beincreased by one cycle.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing. Computer program code for carrying out operations foraspects of the present invention may be written in any combination ofone or more programming languages, including an object orientedprogramming language such as Java, Smalltalk, C++ or the like andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The program codemay execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. Readers will understand that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which includes one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. Each block of the block diagrams and/orflowchart illustration, and combinations of blocks in the block diagramsand/or flowchart illustration, can be implemented by special purposehardware-based systems that perform the specified functions or acts, orcombinations of special purpose hardware and computer instructions.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of memory access alignment in a doubledata rate (‘DDR’) system, the method comprising: executing, by a memorycontroller, one or more write operations to a predetermined address of aDDR memory module; executing, by the memory controller, a plurality ofread operations from the predetermined address of the DDR memory module;and determining, by the memory controller, a read adjust value and awrite adjust value in dependence upon the data captured in response tothe read operations.
 2. The method of claim 1 wherein executing, by amemory controller, one or more write operations to a predeterminedaddress of the DDR memory module further comprises: determining, by thememory controller, a burst length for the write operations, the burstlength comprising the number of bytes that are to be written to anaddress in response to a single write command; and determining, by thememory controller, a number of write operations to execute in dependenceupon the burst length.
 3. The method of claim 1 further comprising:storing, by the memory controller, the read adjust value; andincreasing, by the read adjust value, the number of cycles betweensignaling a subsequent read operation and capturing data from thesubsequent read operation.
 4. The method of claim 1 further comprising:storing, by the memory controller, the write adjust value; andincreasing, by the write adjust value, the number of cycles betweensignaling the DDR memory module of a subsequent write operation andsending to the DDR memory module data associated with the subsequentwrite operation along with the data strobe signal.
 5. The method ofclaim 1 wherein: executing, by a memory controller, one or more writeoperations to a predetermined address of a DDR memory module includesexecuting only a single write operation; sending to the DDR memorymodule a predetermined amount of data of a predetermined pattern alongwith a data strobe signal includes sending two burst lengths of data;and capturing data transmitted from the DDR memory module includescapturing only one burst length of data.
 6. The method of claim 1wherein determining, by the memory controller, a read adjust value and awrite adjust value in dependence upon the data captured in response tothe read operations includes: determining, whether a numerical value ina first unit of the captured data is greater than a numerical value in asecond unit of the captured data; responsive to determining that thenumerical value in the first unit of the captured data is greater thanthe numerical value in the second unit of the captured data, setting theread adjust value to one and setting the write adjust value to thenumerical value in the second unit of the captured data; determining,whether the numerical value in a second unit of the captured data isgreater than a numerical value in a third unit of the captured data;responsive to determining that the numerical value in the second unit ofthe captured data is greater than the numerical value in the third unitof the captured data, setting the read adjust value to two and settingthe write adjust value to the numerical value in the third unit of thecaptured data; determining, whether the numerical value in a third unitof the captured data is greater than a numerical value in a fourth unitof the captured data; and responsive to determining that the numericalvalue in the third unit of the captured data is greater than thenumerical value in the fourth unit of the captured data, setting theread adjust value to three and setting the write adjust value to thenumerical value in the fourth unit of the captured data, otherwisesetting the read adjust value to zero and setting the write adjust valueto the numerical value in the first unit of the captured data.